Conversion of cyclohexane to cyclohexene



United States Patent 3,108,143 CONVERSION OF CYCLOHEXANE T0 CYCLOHEXENE Ralph C. Tallman, El Dorado, Ark., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed May 23, 1960, Ser. No. 30,753

3 Claims. (Cl. 260-666) The present invention relates to the preparation of cyclohexane. More particularly, it relates to the preparation of cyclohexene by the catalytic reaction of oxygen and hydrogen chloride with cyclohexane.

Cyclohexene is a valuable starting material for the production of a wide variety of useful chemical derivatives. It is particularly in demand commercially as a precursor in the manufacture of adipic acid which is important in the synthesis of polyamides such as nylon and to produce caprolactam, another material coming into wide use in the synthetic fiber field. However, cyclohexane does not occur in any substantial quantities in commercially avail-able raw materials and present processes for producing it are economically unattractive or, in general, are not commercially feasible. Since large amounts of cyclohexane are available from petroleum sources, attempts have been made to dehydrogenate this cycloalkane to produce cyclohexene. In most of the processes developed, however, employing a single conversion step, only a very small proportion, e.g., about 5%, can be easily and directly converted to the desired olefin. In the known catalytic processes for conversion of cyclohexane to the corresponding unsaturated cyclic hydrocarbon, the predominant product of dehydrogenation benzene which occurs in proportions that are several times or more as large as the amount of cycloolefin at any reasonable level of conversion per pass.

Another method 'for preparing cyclohexene involves dehydrohalogenation of a halocyclohex-ane particularly a m'onohalo compound. Whether this is done in the vapor or liquid phase, the overall process is a multistage one involving separate operations for halogenating the cyclohexane and for dehydrohalogenating the product which means that difierent apparatus and this is usually complex because of the necessity for temperature regulation, different reaction conditions, different catalysts, etc., are required in the various steps. Thus, the advantages of a process wherein cyclohexane can be converted directly to cyclohexene in a single operation in high yields are immediately obvious.

It is an object of the present invention to provide an improved process for the production of cyclohexene from cyclohexane in a one-step reaction with high yields of cyclohexene and comparatively little loss to non-useful lay-products. Other objects and advantages of the invention will become apparent from the .following description thereof.

According to the invention, a mixture of cyclohexane, hydrogen chloride, and oxygen is contacted at an elevated temperature with magnesium chloride supported upon pumice to produce an effluent gas mixture from which cyclohexene can be readily recovered in excellent yield.

The invention is illustrated in the following example which, however, is not to be construed as limiting it in any manner whatsoever.

Example 1 A tubular glass reactor about 4 ft. long and 40 mm. in diameter wrapped with nichrome wire for heating and covered with asbestos insulation was employed as the reactor. A thermowell containing a thermocouple for measuring temperatures was centrally positioned in the reactor extending throughout its length. The catalyst 3,108,143 Patented Oct. 22, 1963 consisting of magnesium chloride supported upon pumice was charged to the reactor and fluidized by passing nitrogen up through it while the reactor was brought up to reaction temperature. cyclohexane, hydrogen chloride, and air were passed through a horizontal tube packed with glass helices and maintained at a temperature of about C. to vaporize the cyclohexane and preheat the other reactants after which they were introduced into the reactor at rates of approximately 400 per min, 400500 ml. per min., and 1000 ml. per min, respectively. In the reactor, the gases were contacted with the fluidized catalyst (-150 ml.) maintained at a temperature within the range from 470 C. to 520 C. As the reactants were introduced, the flow of nitrogen was proportionately reduced so that the velocity of the entering gaseous reactants helped to maintain the catalyst in a fluidized state. A total of about 38 ml. of cyclohexane was fed over a reaction period of about 15 min.

Efiluent gases from the top of the reactor were passed through a separator filled with glass wool for removal of any entrained catalyst particles and thence into a series of Dry Ice traps and finally through a caustic'scrubber for removal of unreacted hydrogen chloride. Off-gas from the scrubber was vented through a wet-test meter.

The liquid product recovered from the Dry Ice traps contained according to gas chromatographic analysis about 15% cyclohexene. The calculated yield of cyclohexene based on this analysis was 68% Variations in conditions from those given in the example may be made without departing from the scope of the invention. The reaction may be carried out by mixing the cyclohexane with hydrogen chloride and air or oxygen and passing the mixture in contact with the catalyst in a heated reaction chamber; or if desired, the mixture may be introduced into the reaction zone in three separate streams; or the air or oxygen may be introduced into a mixture of the cyclohexane and hydrogen chloride. Precaution should be taken to avoid allowing the cyclohexane and oxygen to reach reaction temperature in the absence of hydrogen chloride.

In the preferred embodiment of the invention, the catalyst is employed in the fluidized or pseudo liquid state. It is maintained in a fluid or suspended state by the gaseous react-ants themselves or optionally, by the use of an additional inert gas introduced from an outside source. The use of a fixed bed operation, however, is not outside the scope of the invention.

The relative proportions of the reactants may vary considerably. Preferred proportions are those coresponding to the stoichiornetic proportions required to eliect monochlorination of the cyclohexane charged, that is, a l:1:0.5 ratio of cyclohexane to hydrogen chloride to oxygen or l:l:2.5 if air is used instead of oxygen. Since hydrogen chloride is not consumed in the reaction, only very small amounts, if any, of this reactant need be fed once the reaction has been initiated if provision is made for recycle of the hydrogen chloride. Excesses of the cyclohexane and air may be employed if desired without significantly affecting the reaction.

Contact time is not too critical and may vary from about 0.5 second to about 12 seconds.

Reaction temperature is a critical tactor and the temperature must be maintained above about 450 C. to efifect the reaction. Preferably, the temperature is maintained in the range from about 450 C. to 520 C. Although temperatures above 520 C. and up to 600 C. can be employed, appreciable amounts of carbon begin to deposit on the catalyst at these higher temperatures.

The catalyst for the process is readily prepared by saturating pumice with a solution, aqueous or otherwise, of magnesium chloride and filtering and drying the impregnated pumice. Further drying may be effected by chloride.

means of a flow of nitrogen (or other inert gas), hydrogen chloride and/or air through the mass of catalyst while it is being heated to reaction temperature after it has been charged to the reactor. A more active catalyst is prepared from a methanolic solution of magnesium Better catalytic activity has also been observed .for a catalyst prepared and dried under vacuum. The catalyst may be readily regenerated by heating with air at a temperature of about 500 C. to burn 01f any deposited carbon from its surface.

What is claimed is.

1. A process for the production of cyclohexene which comprises reacting cyclohexane with hydrogen chloride and oxygen in the presence of a catalyst consisting of magnesium chloride supported upon pumice at a temperature above 450 C.

2. A process for the production of cyclohexene which comprises reacting cyclohexane with hydrogen chloride and oxygen at a temperature in the range from about 450 C. to about 520 C. in the presence of a catalyst References Cited in the file of this patent UNITED STATES PATENTS 2,183,574 Levine et al Dec. 19, 1939 2,308,489 Cass Jan. 19, 1943 2,379,414 Cass July 3, 1945 2,395,314 Blumer Feb. 19, 1946 2,803,679 Conrad Aug. 20, 1957 2,971,995 Ang-anbright Feb. 14, 1961 OTHER REFERENCES Huntress: Organic Chlorine Compounds, John Wiley & Sons, Inc., 1948, page 1104 relied upon. 

1. A PROCESS FOR THE PRODUCTION OF CYCLOHEXENE WHICH COMPRISES REACTING CYCLOHEXANE WITH HYDROGEN CHLORIDE AND OXYGEN IN THE PRESENCE OF A CATALYST CONSISTING OF MAGNESIUM CHLORIDE SUPPORTED UPON PUNICE AT A TEMPERATURE ABOVE 450*C. 